The small size and low cost of CMOS image sensors are increasingly leading to their use instead of CCDs in imaging applications. These advantages of CMOS image sensors may further make imaging practical in several new applications such as in portable communication and computing systems. In particular, as wireless networks expand their ability to carry more data in shorter times, imaging systems may become standard on portable telephones and PDAs to permit users to capture images and transmit the images to remote storage. Such integration of imaging systems requires the image sensors to be low cost, small, and compatible with the manufacturing process of the telephones or other systems containing the image sensors.
Current camera modules containing CMOS image sensors generally include a semiconductor die with microelectronic packaging including a traditional plastic or glass lens that forms an image on the CMOS image sensors on the die. These camera modules make the addition of a complete electronic imaging system a simple operation during manufacture of a telephone or PDA. No lens focusing or other precision optical assembly or testing is required during manufacture of the telephone or PDA because the camera modules come with lenses properly aligned and focused.
The manufacturing of camera modules presents several challenges. In particular, the manufacturing of each module requires several mechanical assembly process steps for centering and aligning one or more far-field lenses. The combined or total tolerances of the mechanical assembly process steps can exceed the allowable maximums that reasonable optical designs dictate. Additionally, the cost of the assembly and particularly the yield loss associated with the mechanical tolerances and contamination during assembly can be high.
Another concern for current camera modules is that the lenses and packaging materials are not compatible with the high solder reflow temperatures associated with lead-free assembly. Accordingly, to satisfy manufacturers' and consumers' desire for lead-free manufacturing and devices, an additional structure such as a flexible circuit or a lead tape is required to keep the module away from the high temperature reflow. Such structures increase the size and cost of camera modules.
Structures and methods are sought for decreasing the manufacturing cost of camera modules containing CMOS imaging sensors and for making camera modules more compact and more compatible with assembly techniques such as high temperature solder reflow processes.